Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains generally to an apparatus and methods to reduce the perception of xe2x80x9cflickerxe2x80x9d by a viewer of three dimensional images on a broadcast television or similar visual display device. The invention can be implemented with a variety of electronic components and. optical transmission materials in the three dimensional viewing glasses. The invention has the primary benefits of: (a) operation with any of the national television broadcast standards in various countries around the world (such as NTSC or PAL); (b) low cost; (c) no viewer adjustment or control required for operation; and (d) compatibility with a variety of optical transmission materials as shutters in the three dimensional viewer glasses, including liquid crystal, ferro-magnetic and other similar materials;
2. Description of the Background Art
A wide variety of glasses for viewing three dimensional images have been developed, known and used since the beginning of three dimensional imaging. These special glasses are essentially all based upon the same principal: blocking the view of one eye while the other eye is shown an image that has been focused and converged on the subject of the optical image from approximately the same angle as that of the corresponding typical human eye looking at the same field of view, then quickly reversing the process so that the opposite eye is blocked from the field of view and the first eye is shown the same image recorded from approximately the same angle as that of the corresponding human eye. The average distance between human eyes is approximately 2.5 inches, and this is the distance that is normally used to separate the two recording devices that are used to create the separate stereo images of the subject matter that are shown to each eye in the above-sequence.
Prior to the relatively recent development of liquid crystal and ferromagnetic materials, the two primary methods of blocking the light (or view) into one eye, while the other eye is able to look the subject filed of view, were electro-mechanical shutters and polarized lenses. Electro-mechanical shutters for three dimensional glasses have largely been replaced due to cost, noise and vibration, and related ergonomic factors. Although polarized filters are still in wide use for three dimensional imaging and viewing, they are not generally applicable to the viewing of images from a standard broadcast television or similar video display system that cannot project polarized light.
The advent of liquid crystal and ferromagnetic materials that can vary from clear to black (little or no light transmission) under an applied dc voltage has revolutionized glasses for viewing three dimensional images. These materials are lighter, lower cost, require no moving parts, and generally give superior image quality. It should be noted that the amplitude and polarity of dc voltage applied to these materials differs from one to another and for the sake of clarity and simplicity in the following discussion the dc voltage (either positive or negative) required to turn one of these electronic materials into the xe2x80x9coffxe2x80x9d or xe2x80x9cno light transmissionxe2x80x9d state will be referred to as the xe2x80x9chighxe2x80x9d voltage and the voltage required to turn such material to its opposite state will be referred to as the xe2x80x9clowxe2x80x9d voltage. It should also, be noted that when liquid crystal material is used, an opposite polarity and equal dc voltage must be applied so that the xe2x80x9ccoloredxe2x80x9d crystalline material does not accumulate on one side (i.e., against one electrode). Thus, in Applicant""s Figures, as in actual operation, an opposite voltage is applied in the corresponding off period for the same electronic shutter.
To Applicant""s knowledge, all of the currently available three dimensional viewing glasses produce a perception by the viewer of xe2x80x9cflickerxe2x80x9d when used with three dimensional images from interlaced video signals used on broadcast television and similar display systems. This flicker is a well known and documented phenomena in the three dimensional imaging industry. Flicker is generally perceived as a very short duration dark flash or blanking of the image in front of the eyes. It is caused by the refresh rate of interlaced video display systems, such as those employed in the various national broadcast television signals, being within the threshold of human perception. In the United States the television video refresh rate is 60 hz, while in Europe, The Peoples""s Republic of China, and Japan for instance, the refresh rate is 50 hz. Three dimensional imaging on such broadcast television systems requires that one eye be essentially blocked from viewing the CRT display every other field. This enables the image of an object in the field of view to be shown to each eye from a slightly different angle (corresponding to the natural separation of human eyes), thereby producing a perception of depth in the subject video image. This blocking of one eye and then the other eye to obtain a perception of depth has the consequence of effectively dividing the effective refresh rate to one-half of the 60 or 50 hz interlaced field rate, that is, to 30 or 25 hz. Such a low effective refresh rate for three dimensional imaging on broadcast television (and similar display systems with a low refresh rate) causes the perception of flicker.
At faster refresh rates, such as those used on certain computer systems and in display systems designed for high definition viewing (such as military, scientific, or other xe2x80x9chigh endxe2x80x9d applications) the human eye perceives little or no flicker from the turning on or off of the shutters in three dimensional viewing glasses. The average person sees little or no flicker once the refresh rate approaches 80 or more hz.
As a consequence of the flicker problem inherent in broadcast television due to the low refresh rates, three dimensional viewing on broadcast television has not gained a strong foothold amongst the viewing population. Numerous studies and attempts have been made to eliminate or reduce the flicker effect, including contrast filters, and other devices and methods. However, to applicant""s knowledge, none of these efforts has been commercially successful.
Applicant""s invention approaches the flicker problem in a novel and original manner that substantially reduces the perception of flicker in three dimensional images viewed on standard broadcast televisions and similar display systems. In addition, applicant""s invention can be used with different types of shutter materials such as liquid crystal or ferromagnetic devices. However, as discussed below, Applicant""s invention describes the use of a particular liquid crystal material as an electronic shutter that, under certain lighting and viewing conditions, further reduces the perception of flicker.
The present invention consists of an apparatus and methods to reduce the perception of xe2x80x9cflickerxe2x80x9d by a viewer of three dimensional images on a broadcast television or similar visual display device. This apparatus and method controls the dc voltages applied to the electronic shutter such that for each eye, the amount of light transmission through the electronic shutter is in the range of a xe2x80x9cwindowxe2x80x9d defined by the xe2x80x9chighxe2x80x9d and xe2x80x9clowxe2x80x9d dc voltages applied to the shutter. The xe2x80x9clowxe2x80x9d dc voltage is set at a level that permits sufficient light for the viewer to perceive a three dimensional image during the xe2x80x9conxe2x80x9d period, and the xe2x80x9chighxe2x80x9d dc is set to allow a certain amount of light to continue to pass through the electronic shutter so that the viewer does not see the image in front of the respective eye turn completely black or totally opaque. [Note, as discussed below, the actual voltages applied may be reversed if different liquid crystal or other transmission material is employed.]
In addition, the present invention consists of a an electronic circuit that controls the beginning and end of the shutter on and off periods (corresponding to the odd and even fields of interlaced video) in such a manner as to permit the leading and trailing edge of the high and low voltages applied to the shutters in Applicant""s invention to be precisely controlled and adjusted to a position where the transmission of light through the shutters is optimized for minimum flicker.
In addition, the present invention consists of a an electronic circuit that controls the rise and fall times of the high and low voltages applied to the electronic shutters in such a manner as to control the current (or charge) applied to the electronic shutters at the leading and trailing edge of each on or off period, thereby enabling a feathering effect that further reduces flicker.
In addition, the present invention consists of variable resistors in series with the liquid crystal shutters so as to slow down the rise and fall times of the current (or charge) in the liquid crystal shutter, thereby permitting additional adjustment of the phase of the light transmission window.
In addition, the present invention consists of the use of liquid crystal shutters that are normally white and opaque with no dc voltage applied and that turn clear as a high dc voltage is applied. The white liquid crystal shutter, under certain lighting, viewing and content conditions can reduce the effect of xe2x80x9cflickerxe2x80x9d because there is less contrast between the eye seeing white opaque, then clear, as opposed to the eye seeing clear, then black, as with the other liquid crystals used in the industry.
Considered in view of prior designs, Applicant""s invention significantly improves the state of the art of glasses (eye sets) for the viewing of three dimensional images on broadcast televisions and similar CRT or display devices.
One object of the invention is to produce three dimensional viewing glasses that reduce the perception of xe2x80x9cflickerxe2x80x9d when used with a broadcast television or similar CRT or other display device.
Another object of the invention is to produce three dimensional viewing glasses that have an adjustable maximum and minimum drive voltage for the liquid crystal (or other type of) shutters.
Another object of the invention is to produce three dimensional viewing glasses that have an adjustable time delay from the vertical sync signal for the liquid crystal (or other type of) shutters.
Another object of the invention is to produce three dimensional viewing glasses that have an adjustable current rise and fall times for the voltage waveforms that drive the liquid crystal (or other type on shutters.
Another object of the invention is to produce three dimensional viewing glasses that have variable resistors in series with the electronic shutters that affects the current rise. and fall times for the voltage waveforms that drive the liquid crystal (or other type of) shutters.
Another object of the invention is to produce three dimensional viewing glasses that have liquid crystal shutters that are normally opaque white (when no voltage applied) and that turn clear when a voltage is applied.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.